Biological tests are used at the present times in the medical, clinical and research fields to monitor and quantify the biological activity of activating or inhibiting factors which cannot be otherwise identified and quantified reliably with other laboratory techniques.
To carry out such biological tests, it is necessary to use animals or cellular cultures and, in the latter case, to subject the cells at times to a step of preliminary preparation called the "starvation" or "privation" step, in which the cells are bred in complete absence of a hormone, which is then used as a stimulator to increase the sensitivity of the cells to that hormone.
The cells which have undergone the "starvation" or "privation" step are called "cells in the ready state".
The sensitization is also effective in the same manner as regards pathological stimulators such as the thyroid-stimulating auto-antibodies (TSab).
This "privation" step has a duration which can be varied according to the type of tests and which lasts at least for some days, generally between about 5 and 10 days.
A first method arranges to keep the colonies of cells continually in incubation until the moment of performance of the test.
This method entails a plurality of drawbacks such as the high cost arising from the consumption of the culture medium required for maintaining cells always ready for possible tests, the danger of contamination of the culture medium with a resulting lack of validity of the tests carried out, the need to ensure the maintaining of sterility during the whole period of starvation, the need to change the medium, the maintaining of standard conditions during the whole period and the difficulty of transferring the cultures to a distance.
Moreover, this method of extempore production of the cultures when required does not ensure a production of homogeneous and reproducible cultures with the consequence that the results achieved with cultures produced at different periods and/or at different places cannot always be completely compared to each other.
So as to avoid some of these problems, a method is sometimes used whereby the cultures are frozen before the starvation step.
This second method, on the one hand, reduces the costs of the additives required during the cultivation of the cultures but, on the other hand, does not solve the problems linked to the long times of the starvation period and to the standardization of the final product.
In particular, this method consists in freezing at a temperature of at least -80.degree. C., but typically at temperatures of about -196.degree. C. in liquid nitrogen, the cells which have to be used.
These frozen cells, so as to be used, have to be subjected to thawing and to a successive period of recovery during which the cells are deposited on, and possible adhere to, the plastic bottom of the container and then undergo the starvation step.
This period of recovery may last even for some days, which have to be added to the time of the starvation step and which prolong further the times of preparation of the cellular cultures.
Moreover, this method does not make possible a standardization of the samples that ensures the complete reproducibility of the experiments, and therefore restricts the validity of the latter.
Furthermore, another very important problem which has still not been overcome arises from the fact that up to the present time only the laboratories duly equipped and expert in cellular cultures are able to carry out biological tests on cells in vitro, namely the so-called bio-assays, since only those laboratories are able to produce and to keep alive the cellular cultures required for carrying out such tests.
The present applicants have studied, tested and obtained this invention so as to overcome the shortcomings of the state of the art and to achieve further advantages.